Signaling by erbB tyrosine kinase receptors plays a pivotal role in normal development and disease processes including cancer. The long-term objective of this work is to identify the targets of erbB signaling and determine how they effect different cell responses such as division or differentiation. This proposal describes the use of hybridization to cDNA microarrays to document gene expression patterns in response to changes in erbB-receptor signaling in Drosophila. The results are expected to identify novel targets of the pathway, gene targets specific to particular ligands, and to reveal connections to other signaling pathways. Drosophila will be used to allow rapid genetic analysis of new genes and gene interactions, however, the strong conservation of erbB-signaling pathways in vertebrates and Drosophila suggests this information will also be relevant to vertebrates. ErbB-target genes are potential candidates for cancer therapy.